A powerful winter storm system has pounded the American heartland and headed toward the Northeast, where people braced for the high winds and heavy snow that disrupted holiday travel, knocked out power to thousands of homes and were blamed in at least six deaths.

Over 1000 flights were cancelled or delayed, scores of motorists got stuck on icy roads or slid into drifts, and blizzard warnings were issued amid snowy gusts of 48kph that blanketed roads and windshields, at times causing whiteout conditions.

"The way I've been describing it is as a low-end blizzard, but that's sort of like saying a small Tyrannosaurus rex," said John Kwiatkowski, a meteorologist with the National Weather Service in Indianapolis.

Two passengers in a car on a sleet-slickened Arkansas highway died when the vehicle crossed the centre line and struck an sport utility vehicle.

In Oklahoma, the Highway Patrol said a 76-year-old woman died Christmas Day when a truck crossed into oncoming traffic and hit the car she was in. The Highway Patrol earlier reported that a 28-year-old woman was killed in another crash.

The storm's winds were also blamed Tuesday for toppling a tree onto a truck in Texas, killing the driver, and a tree onto a house in Louisiana, killing a man.

About 1400 flights nationwide had been cancelled by near midday Wednesday, according to flight tracking site FlightAware.com. More cancellations were likely, with Washington, New York and Philadelphia expected to see the most problems.

The system, which spawned Gulf Coast region tornados on Christmas Day and a historic amount of snow in Arkansas, pushed through the Upper Ohio Valley and headed toward the Northeast. Forecasts called for 12 inches to 18 inches (300 to 457mms) of snow inland from western New York to Maine starting late Wednesday and into Thursday and tapering off into a mix of rain and snow closer to the coast, where little accumulation was expected in such cities as New York and Boston.

Thirty-four tornados were reported in Texas, Louisiana, Mississippi and Alabama during the outbreak, the National Weather Service said. The storms left more than 100,000 in the region without power for a while, darkening Christmas celebrations.

Camera footage captured the approach of the large funnel cloud in Mobile, Alabama, the biggest city hit by numerous twisters.

A large section of the roof on the city's Trinity Episcopal Church was missing, said Scott Rye, a senior warden at the church.

On Christmas Eve, the church with about 500 members was crowded for services.